Precision comparator



sp:.22,192s. n 1,554,392

F. C. WEAVER PRECISION COMPARATOR mad on. 2a, 1922 INVENTOR. y

176. zas/ar.

. W ATTORNEYS.

Patented Sept. 22, 1925.

UNITED STATES PATENT OFFICE.

FLQYDKC. WEAVER, QF WASHINGTON, DISTRICT 0F COLUMBIA.

-raEcIsIoN compararon;

Applica'tloixled October 28, 1922'. Serial No. 597,572.k

gage blocks, with all the-precision attain-l able by interferometerequipment at ordinary temperatures and under ordinary conditions by onlythe average skill and assistance to be found in a high tool departmentor of 'a measurmg laboratory.

Another object of this invention is to provide a means of comparison oftwo dimensions simultaneously by light interference methods, such thatan ordinary operator unf der ordinary conditions can make thesecomparisons readily, accurately and of the limit of interferencecomparisons of a few, millionths of an inch, and using no accessorytools, but simply by noting certain indicating means on t e device. Onepractical form of construction an assembly of the` resent 'inventionwill be hereinafter descri d and is lillustrated in theaccompanyingdrawing, in which F Fig. 1 is a side elevation of therecision comparator, partly insection an partly broken away, and f Fig.2 is a sectional View taken on the line 2 2 of Fig. 1 and looking in thedirection of the arrows.

In the accompanying drawing the numeral 1 indicates an u er interferencesurface which-is preferahy y formed of transparent glass but may beformed of any suitable transparent material. This interference surfaceis formed as a circular disc which is of an even thickness at all pointsto 'provide parallel upper-and lower faces. The lower interferencesurface 2 is also formed as a circular disc which is of the samethickness as the disc 1 and provided with parallel upper and lowerfaces. This lower disc is however a great deal smaller than the disc 1and may be formed of transparent or opaque material. A scale 4 has beenshown provided upon the disc 2 but it will be understood that it may beprovided grade machine upon the disc 14 instead of the disc 2 if sodesired. By this arrangement of scale 4 can be viewed when looking downupon the disc 4 and Haidinger fringes which' 60 will appear whenmono-chromatic light is directed upon the upper disc may be com-.- paredwith the scale.

These Haidinger fringes will' be referred vto hereafter as interferencecircles asin 'some cases the disc will be formed with curved faces andNewtons rings would then appear instead of Haidinger fringes.

These rings will be centered upon the scale and by moving the eye fromone end of the scale to the other the size of the rings can be observed.If the rin sremain the same size the discs will then e exactly parallelbut if the discs arenot parallel the rings will increase or decrease indiameter according to the direction in which Vthe upper disc is tilted.This will bemore fully brought out when the operation of the apparatusis set forth.

In order to mount the discs there has been provided a cell or casinghaving a base 14, an annular wall 9 and an upper ring 22 securedupongthe wall 9 by screws 23 and providing an inwardly extending annularlends engaging the disc as shown so that by properly adjusting thescrews 12 and 13 the disc can be supported` in a horizontal plane. Thedisc 1 is to be tiltable in the casing and therefore has been mountedbetween pivot pins 10 and at one point rests upon a pin 5 which isthreaded through the upper web 8' and corresponds to the pin 12. Sockets3 are mounted inthe base at opposite sides of the recess in which thedisc 2 is mounted and each is provided with a base in which is slidablymounted a pin 6 which correspond to the ins 13 and are to engage theunder face ofpth'e disc 1 so that this disc can be held in a horizontalplane or be allowed to tilt. to one side or the other. Each of thesepins 6 passes through a bushing 24 and above the bushing is providedwith spaced collars 25 which provide an annular pocket parts the' 26 toreceive an eccentric pin "'29 extending from the inner end of a key 2S.This key 2H is' rotatable in the socket 3 and is provided with a handle2T so that the key may be rotated to move a pin 6 vertically. Thispermits the blocks to be put in place.

This casing is to be mounted above a plat forni 20 which has a [latupper surface and is to constitute a master surface in that it is to beexactly horizontal and is to support a measuring block 7 and a block tobe measured. This platform 2O rests upon a base 1S having radiating armscarrying friction pads 19 and is held in place by a screw Q1 whichprojects upwardly through the base axially thereof. One arm of this haseis provided with a threaded socket into which the threaded lower end ofa post 17 is rcceived and this post is circular in cross section so thatit may slidably receive the clamp portion 16 of the bracket arm 15 eX-tending from the casing. This clamp portion will be provided with theusual adjusting screw so that it may be secured in a set position uponthe post with the casing at the desired distance above the mastersurface or platform 20.

lVhen this device is in use the casing will be set at the properdistance above the platform according to the size of the blocks to bemeasured and a master block 7 of a known height will be placed upon theplatform and thelower end of one pin 6 allowed to rest upon the upperend of the master or measuring block.

The block to be measured is then placed upon the platform beneath thesecond pin 6 and will have its upper end engaged by this second pin. Theupper ends of the pins will engage the under face of the disc 1 and ifthe bocks are of the same height the disc 1 will be parallel to the disc2 whereas if the block to be measured is taller or shorter than themaster block the disc 1 will be tilted to one side or the other. Thiscan be accurately determined by observing the interference rings whichthe light projected onto the disc causes to appear above the scale 4.While. looking down upon the disc, the eye is caused to travel from oneend of the scale to the other and if the rings remain the same size atall points along the scale the two discs are parallel and it .will beknown that the blocks are of the same height. If the block to bemeasured is taller than the master block then the disc 1 at this end ofthe scale is a greater distance from the disc 2 than at the other endand this tilting away from the disc 2 causes the rings to increase insize towards this end of the scale. If the block to be measured isshorter than the master block the disc 1 at this end of the scale iscloser to the disc 2 and therefore the rings will be reduced in size asthe eye moves along the scale.

A table can be worked out so that when a dill'erence in the size of aring is observed the table will give the variation in the height of theblock being measured. This varial ion may by the use of this device becomputed to a very minute fraction of an inch. It will therefore be seenthat the blocks can be very accurately measured.

The invention having been described, what is claimed is:

1. In a device of the character described, a master surface, verticallyadjustable pins mounted above the master surface, and interferencesurfaces positioned above the` master surface in superimposed relationto each other. one being held parallel to the master surface and theother tiltably mountcd and controlled in its tilt ing moven'ient by saidpins and one of said. interference surfaces having gage markingsthereon.

2. In a. device of the character described, a master surface, a cell, asupporting structure for the master surface and cell, interferencesurfaces in said cell in superimposed relation, one being stationary andthe other tiltable and one being provided with gage markings, andvertically movable pins carried by said cell for having their lower endsengaging articles placed upon the master surface and their upper endsengaging the tiltable interference surface at opposite sides of its lineof pivotal mounting.

3. In a device of the character described, a master surface, a cell,means for supporting the master surface and cell, interference surfacescarried within said cell, one of the interference surfaces beingprovided with gage markings and one being tiltable. vertically movablepins carried by said cell, and means for shifting said pins, thetiltable interference being supported by said pins and the pins beingadapted to engage the upper surfaces of articles placed upon the mastersurface whereby tilting of the tiltable interference surface may becontrolled by the height of the articles With respect to each other.

4. In a device of the character described, the combination of a mastersurface, a cell, means for supportingsaid master surface and said celland adapted to rest upon the upper surfaces of articles resting upon themaster surfaces, vertically movable pins carried by said cell, said pinshavin enlarged bosses provided with horizonta grooves, levers havingShanks provided with eccentrically arranged pins extending into saidgrooves, whereby when the levers are swung the first-mentioned pins willbe shifted, and interference surfaces carried within said cellinsuperimposed relation, one of the interference surfaces having gagemarkings thereon and one being plvotally mounted and restingr upon thevertically movable pins and adapted to be moved into and out of a planeparallel to the master surface and other interference surface bythemovable pins.

5. In a device of the class described, the combination of a supportingsurface and a celL means for supporting said surface and said cell, saidcell being circular and having a base and a web lextending above thebase, bushings carried by said base, vertically adjustable pins carriedby said bushings and extending into said cell, the lower ends of saidpins being adapted to engage the upper faces of articles resting uponthe supporting surface, and adjustable screw carried by said Web, anupper interference surface resting upon said pins and said screw,vertically adjustable screws and points carried by said base, a lowerinterference surface positioned wit-hin said cell and resting upon saidlastmentioned screws and points and being positonedbetween said firstmentioned pms, horizontally extending screws carried by said cell andthe web thereof and engaging the peripheries of said interferencesurfaces for holding them from shifting laterally, and gage marks uponone of said interference surfaces, all as and for the purposes setforth.

In testimony whereof I hereunto alix my signature.

FLOYD C. WEAVER.

